Terrestrial plants are a proven source for effective cancer chemotherapeutic agents. However, for novel drug discovery, major challenges include identification of correct starting materials and provision of a proper bioassay procedure for procurement of truly useful active principles. This project provides an experimental strategy and the where-with-all to meet these challenges. As a first level of selection, cytotoxic plant extracts will be identified in a panel of cultured mammalian cells. Of the 500 plant extracts to be evaluated each year, it is responsible to suggest 50 can be classified as active (cytotoxic) and the remaining 450 can be classified as inactive (non-cytotoxic). The 450 non- cytotoxic extracts will be evaluated in secondary models to assess anti- metastatic and anti-angiogenic potential. Specifically, potential to block cancer cell invasion will be determined with Matrigel cell migration test systems and growth inhibitory potential will be assessed with cultured human umbilical vein endothelial cells (HUVEC). We anticipate these evaluation procedures will identify 3-5 promising leads per year that will be subjected to bioassay-directed fractionation using the appropriate in vitro system as a monitor. For the 50 cytotoxic leads, a straight-forward preliminary fractionation will be performed (Project 2) to yield a cytotoxic fraction with enriched activity. These 50 susceptible cell lines, to provide an initial indication of anti-tumor potential. It is anticipated this will eliminate approximately one-half of the test materials, yielding 25 active leads. These 25 leads will be further assessed for potential to modulate gene expression. Using a susceptible cultured cell line and DNA array analyses, the effect of each lead material on the expression of approximately 1,000 cancer-related genes will be determined. Based on these data sets, a judicious decision can be made regarding our 3-5 best lead starting materials, which will be subjected to bioassay-directed fractionation (Project 2) using a susceptible as a monitor. The chemical isolates will be evaluated with the in vitro and animal models used to facilitate their discovery. As a consequence of this strategy, we anticipate virtually all resulting isolates will be clinical or mechanistic significance.